DRA Resource Availability Visibility

This KEP addresses a visibility gap in Dynamic Resource Allocation (DRA) by enabling users to view available device capacity across resource pools. While ResourceSlices store capacity data and ResourceClaims track consumption, there is currently no straightforward way for users to view the available capacity remaining in a pool or on a node. This enhancement introduces a ResourcePoolStatusRequest API following the CertificateSigningRequest (CSR) pattern: 1. User creates a ResourcePoolStatusRequest object specifying a driver (required) and optional pool filter 2. A controller in kube-controller-manager watches for new requests 3. Controller computes pool availability and writes result to status 4. User reads the status to see pool availability 5. To recalculate, user deletes and recreates the request This in-tree approach was chosen based on API review feedback to: - Provide an always-available, in-sync solution with Kubernetes releases - Follow established patterns (CSR, device taints with "None" effect) - Control permissions via standard RBAC on the request object - Avoid continuous controller overhead (one-time computation per request)